In the manufacture and use of multilayer elements useful in radiographic, magnetic, electrographic or photographic processes and products, the generation of static electrical charge is a serious problem. In the case of photographic and magnetic products, the most serious deleterious effects are evident when accumulated charge discharges, producing either actinic radiation or "noise" which is recorded as an image on photosensitive products or as static on magnetic products such as magnetic tape. In the case of electrographic products, such discharges can diminish image quality and cause elements to stick to each other or to other surfaces. Static discharge can occur in the course of manufacturing processes (e.g. coating, finishing or packaging) or during customer use (e.g. in cameras, printers, tape recorders, copier/duplicator equipment, etc.).
Accumulation of static electrical charge on elements designed for electrographic use increases the tendency of such elements to stick to each other when stacked together or when being used. Many times, what is known as a "multifeed" occurs when two or more elements, which have been drawn into the electrographic copier/duplicator equipment, stick together and jam in the feeder rollers. Another problem arises when such elements stick to each other or to other surfaces within the equipment during the electrographic copying process. Typically, the element sticks at the fuser station where a toned image on the element is fused and jams that station causing equipment shutdown. Therefore, it is often difficult to feed such elements into and through electrographic copier/duplicator equipment smoothly and reliably.
It has been known for many years that the projection of an image present upon a transparency may serve as an effective means for conveying information to one or more viewers. Such projection-viewable transparencies can be prepared by a number of methods, a common one being transfer electrostatic copying. By this process, an image of fusible toner particles is formed on an image-receiving layer of a transparent image-receiving element. The particles are then fixed to the element in some manner, e.g. by contact with a heated fusing surface. This process usually occurs inside electrographic copier/duplicator equipment (sometimes known as a copier/duplicator), such as that described in, for example, U.S. Pat. No. 4,099,860 (issued July 11, 1978 to Connin). It is apparent that image-receiving elements used in such a process and equipment must contact a variety of components (e.g. rollers, plates, belts, etc.) in such equipment. If any element "sticks" either to any of these components or to another element, it can "jam" up the entire copying process and impede the movement of or cause damage to itself and other elements, thereby greatly increasing equipment maintenance problems.
It has been observed that "multifeeds" and "jams" at the fuser station have been occurring with increasing frequency with currently-available transparent image-forming elements that are utilized in such copier/duplicator equipment. While certain equipment changes can remedy some of the causes of such malfunctions, the number of such malfunctions is still undesirably high. It is believed that these problems are due largely to the accumulation of static electrical charge on the elements. Some users have attempted to reduce the incidence of "multifeeds" by interleaving the transparent image-receiving element with sheets of paper. This, however, results in lower productive use of the copier/duplicator equipment and additional labor costs for adding and removing the paper sheets.
It is known that static electrical charge build-up can be minimized in multilayer elements (both sensitized and nonsensitized) by including an antistatic layer in such elements. Examples of antistatic compositions used for this purpose are described, for example, in U.S. Pat. No. 3,437,484 (issued Apr. 18, 1969 to Nadeau). Such compositions have resolved the static accumulation problem to a significant degree in many multilayer elements, including transparent image-receiving elements known in the art, such as those described in U.S. Pat. Nos. 3,549,360 (issued Dec. 22, 1970 to O'Neill et al) and 4,259,422 (issued Mar. 31, 1981 to Davidson et al). In Davidson et al, the transparent image-receiving elements are described as having a transparent polymeric support having on one side a hydrophilic colloid-containing image-receiving layer and on the other side the antistatic composition described in the Nadeau patent mentioned previously.
It has been found that, as advances are made in electrographic copier/duplicator equipment design, higher speed electrographic copying is possible. High speed copying is desirable to increase productivity. However, it has been observed that high speed copying using currently-available transparent image-receiving elements has resulted in sharply higher incidences of element "multifeed" and "jams" within the equipment. It has also been observed that projection-viewable transparencies made from such elements cling to each other when they exit the equipment. Hence, they can not be stacked neatly and packaged without tediously pulling each element from the others and restacking. Such problems are believed to be due to higher accumulated static electrical charges on the elements resulting from higher copying speeds. Attempts to reduce these accumulated charges with known antistatic compositions have met with little success.
Hence, there is a need in the art for multilayer elements having a reduced propensity for accumulating static electrical charge, and particularly for transparent image-receiving elements that can be fed and transported smoothly and reliably through electrographic copier/duplicator equipment at high speeds without significant accumulation of static electrical charge.